<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no;">
    <title>Title</title>
</head>
<body>

<!--宽高可以根据内容变化-->
<canvas id="myCanvas" style="border:1px solid #c3c3c3;">
    Your browser does not support the canvas element.
</canvas>

<script type="text/javascript">

    var c=document.getElementById("myCanvas");
    var cxt=c.getContext("2d");
    cxt.moveTo(10,10);
    cxt.lineTo(150,50);
    cxt.lineTo(10,50);
    cxt.lineTo(10,10);

    cxt.stroke();

</script>


</body>
</html>